Effects of surgical correction of class III malocclusion on the pharyngeal airway and its influence on sleep apnoea

Abstract

The objective of this study was to evaluate, through cone beam computed tomography, the immediate changes in pharyngeal airway space (PAS) after orthognathic surgery in class III patients, and to determine the influence of surgery on the development of obstructive sleep apnoea hypopnoea syndrome (OSAHS). A prospective study was conducted; 33 patients were divided into three groups: mandibular setback surgery (nine patients), bimaxillary surgery (18 patients), and maxillary advancement surgery (six patients). PAS measurements obtained pre- and postoperatively were compared using the t -test. All patients were assessed clinically for OSAHS before surgery and at 6 months postoperative using the Berlin questionnaire and a combined clinical assessment, which included the assessment of OSAHS symptoms, Epworth Sleepiness Scale score, and body mass index. Patients undergoing isolated mandibular setback surgery demonstrated a decrease in total PAS volume, in hypopharynx volume, and in minimum cross-sectional area of the pharynx immediately after surgery ( P < 0.05). The clinical analysis did not reveal signs or symptoms of OSAHS in any of the 33 patients. Although patients who underwent mandibular setback surgery alone demonstrated a volume reduction in the PAS and a decrease in minimum cross-sectional area, these reductions were not accompanied by signs or symptoms of OSAHS.

Orthognathic surgery is applied to correct severe class III malocclusions, and changes in the pharyngeal airway have been observed following this procedure. In mandibular setback surgery, three-dimensional (3D) modification of the jaw results in a reorganization of the pharyngeal wall, and it has been suggested that this new relationship of the upper airway may compromise the air flow and predispose the patient to obstructive sleep apnoea hypopnoea syndrome (OSAHS). This syndrome is a risk factor for several diseases, including hypertension and cardiac arrhythmias, and might increase morbidity and mortality. Therefore narrowing of the pharyngeal airway space (PAS) after orthognathic surgery has gained increased attention in recent years.

The diagnosis of OSAHS begins with a clinical examination of the patient, and many techniques have been used for this purpose. The Berlin questionnaire is currently the most widely used screening tool for identifying this syndrome. Similarly, the Epworth Sleepiness Scale (ESS) measures the level of drowsiness and is an important screening tool; a score is generated from the patient’s responses to a questionnaire. Both questionnaires are helpful for selecting patients who may require polysomnography for a definitive diagnosis and for the quantification of the severity of the syndrome.

Only a few studies have used cone beam computed tomography (CBCT) to investigate the complex 3D anatomical modification in class III patients. A recent meta-analysis provided evidence that mandibular setback surgery alone is associated with a notable decrease in the PAS, both at the level of the soft palate and at the base of the tongue. However, evidence is lacking on airway volume changes after orthognathic surgery, and more studies are necessary. Similarly, there is no evidence to confirm that bimaxillary or mandibular setback surgery predisposes the patient to OSAHS.

The aim of this study was to evaluate the immediate changes in pharyngeal airway volume in class III patients undergoing different orthognathic procedures (mandibular setback surgery, bimaxillary surgery, and maxillary advancement surgery), and to analyze the influence of orthognathic surgery on the development of OSAHS.

Materials and methods

A prospective observational study was conducted to identify the possible development of OSAHS after orthognathic surgery to correct class III malocclusions. Measurements of the PAS on CBCT scans and two screening tools for OSAHS (the Berlin questionnaire and a combined clinical assessment) were used. Inclusion criteria were (1) healthy patient (American Society of Anesthesiology (ASA) I or II); (2) the presence of a skeletal class III malocclusion; and (3) CBCT scans obtained and questionnaires answered at the previously designated time points. Exclusion criteria included (1) patients presenting a significant increase in body mass index (BMI) during the study period; (2) prior diagnosis of OSAHS; and (3) history of adjuvant surgery in the soft tissues of the head and neck region.

Surgeries were done at a university hospital in Rio de Janeiro State, Brazil. The orthognathic surgery was performed by an oral and maxillofacial team, and all patients underwent internal fixation with titanium miniplates and screws. This study was approved by the necessary ethics committee. The patients provided informed consent before surgery.

A standardized CBCT scanning protocol was used (i-CAT; Imaging Sciences International, Inc., Hatfield, PA, USA); scans were obtained between March and December 2014. The patients were instructed to sit upright in natural head position with the help of a mirror. The mandible was positioned in centric relation without the use of any device and only with manual manipulation. The tongue was required to be in a relaxed position, and the patient was asked to breathe slowly and not to swallow.

Standardization of the head orientation was performed in Dolphin Imaging version 11.7 Beta software (Dolphin Imaging and Management Solutions, Chatsworth, CA, USA) as follows: the mid-sagittal plane seen in frontal view passed through the anterior nasal spine, and infra-orbital points were used to guide the axial plane. On the right side of the skull, the axial plane passed through porion and the infra-orbital points, and finally in the superior view of the skull, the median sagittal plane passed through crista galli and the basion point.

All PAS measurements were performed by the same operator using the Dolphin Imaging program. All measurements were done three times, at 1-week intervals; a maximum of 10 CBCT scans were evaluated on the same day. The mean values of the three measurements were compared at different time points (T0 pre-operative and T1 immediately after surgery (at 10 days)), and subjected to statistical analysis. An intra-examiner analysis was also done to evaluate the reproducibility of the measurements.

Four volumetric measurements were obtained: (1) total volume of the PAS, (2) volume of the nasopharynx, (3) volume of the oropharynx, and (4) volume of the hypopharynx. The minimum cross-sectional area (CSA) of the pharynx was determined and measured automatically by the software. The anatomical limits for these spaces are described in Table 1 . Pre- and postoperative volume measurements of each of the four regions, as well as the minimum CSA, were compared using the paired t -test. A P -value of less than 0.05 was considered significant.

Table 1
Limits of the pharyngeal airway space.
Region Limits Anatomical limits
Nasopharynx Anterior Frontal plane perpendicular to FH passing through PNS
Posterior Soft tissue contour of the pharyngeal wall
Upper Soft tissue contour of the pharyngeal wall
Lower Plane parallel to FH passing through PNS and extending to the posterior wall of the pharynx
Lateral Soft tissue contour of the pharyngeal lateral wall
Oropharynx Anterior Frontal plane perpendicular to FH passing through PNS
Posterior Soft tissue contour of the pharyngeal wall
Upper Plane parallel to FH passing through PNS and extending to the posterior wall of the pharynx
Lower Plane parallel to FH plane passing through C3ai
Lateral Soft tissue contour of the pharyngeal lateral wall
Hypopharynx Anterior Frontal plane perpendicular to FH passing through PNS
Posterior Soft tissue contour of the pharyngeal wall
Upper Plane parallel to FH plane passing through C3ai
Lower Plane parallel to FH plane passing through C4ai
Lateral Soft tissue contour of the pharyngeal lateral wall
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Dec 15, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Effects of surgical correction of class III malocclusion on the pharyngeal airway and its influence on sleep apnoea
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